Messages in this thread Patch in this message | | | Date | Fri, 8 May 2015 16:24:53 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: tell the world boot_params is 16-byte aligned |
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On Fri, May 08, 2015 at 03:42:33PM +0200, Rasmus Villemoes wrote: > It doesn't matter much, but this disassembly makes me cry a little bit: > > ffffffff81f21223 <copy_bootdata>: > ffffffff81f21223: 55 push %rbp > ffffffff81f21224: 48 c7 c0 40 c2 02 82 mov $0xffffffff8202c240,%rax > ffffffff81f2122b: 48 89 fe mov %rdi,%rsi > ffffffff81f2122e: a8 01 test $0x1,%al > > The reason is that boot_params is defined with > __attribute__((aligned(16))) in boot/main.c, but other translation > units only see the packed attribute on the definition of struct > boot_params, so assume the worst. Making the de facto alignment public
Wouldn't it be better if we put both attributes together, i.e.:
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h index ab456dc233b5..d26953d896d2 100644 --- a/arch/x86/include/uapi/asm/bootparam.h +++ b/arch/x86/include/uapi/asm/bootparam.h @@ -155,7 +155,7 @@ struct boot_params { __u8 _pad8[48]; /* 0xcd0 */ struct edd_info eddbuf[EDDMAXNR]; /* 0xd00 */ __u8 _pad9[276]; /* 0xeec */ -} __attribute__((packed)); +} __attribute__((packed, aligned(16))); enum { X86_SUBARCH_PC = 0, --- so that they're concentrated in one place?
gcc seems to swallow it, I haven't checked the bloat decrease though, when one would declare boot_params this way.
Thanks.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply. --
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